Pump for liquids



Dec. 3, 1963 P. T. GILBERT, JR

PUMP FOR LIQUIDS Filed March 21, 1960 FIG. 1.

INVENTOR PAUL. THO/was GIL-BERT, JR.

i xviiv BY l-l/S ATTORNEYS HARE/$ K/gcfl, @1555 a- KERN 3,112,882 PUMPFtllit LllQUiDd Paul Thomas Gilbert, .ln, Fullerton, Calii, assigns: to

l'eclnnan instruments, inc, a corporation of (latiiornia Filed Mar. 2.1,196d, Ser. No. 16,373 6 Claims. (til. 239-273) This invention relates toa pump for generating a continuous and uniform flow of liquid. Whereasit is particularly elfective for generating very low flow rates, such as0.01 ml./min., and has been used for rates up to 3 ml./min., its utilityis not necessarily confined to this range. Further, whereas the pump isparticularly adapted for feeding sample to a flame for purposes offlamespectrophotometric analysis, it is not limited to this application.

ln flame photometry, the sample is most commonly supplied to the flameby means of a pneumatic atomizer. The suction created by the Venturieffect of a stream of gas flowing at high speed past or around the endof a capillary tube causes liquid, applied to the other end of the tube,to flow through it, being atomized on emerging into the stream of gas.The device thus serves the dual purpose of pumping the liquid andatomizing it. The gas used for atomization conveys the spray to theflame, of which it forms one of the constituents. A typicalatomizer-burner is shown in my U.S. Patent No. 2,714,833.

In pneumatic atomization, the rate of liquid flow depends upon and isusually proportional to, the suction, which in turn is governed by therate of gas flow. The liquid flow rate thus cannot be controlledindependently of the flow of gas that supplies the flame. This isinconvenient, for it is desirable in any such technique to haveindependent control of the significant variables, to permit theirseparate optimization. Accordingly, it is an object of the presentinvention to provide a pump for liquid having an independent control offlow rate.

Further, in pneumatic atomization the liquid flow rate will be alteredby any accidental alteration of the gas flow rate, such as results frompartial clogging of the gas port by dirt; or by any accidental change ofconfiguration of the parts of the atomizer, such as results from thermalexpansion of parts on heating by the flame, shifting of an insecurelyfastened capillary, or accumulation of deposits (e.g., salts left byevaporation of the sample solution) upon the tip of the capillary or gasport. The liquid flow rate is also affected by the effect of nature ofthe gas and of the liquid itself upon the suction. Thus, the pres enceof hydrogen, which diffuses very rapidly, in the proximity of thecapillary tip will drastically reduce the suction. If hydrogen is usedfor atomization, it will generate much less suction than an equal flowof heavier gas. Since the liquid itself forms part of the environment oft e capillary tip, it is likely that different liquids, with theirdifierent vapor pressures, densities, etc, will somewhat affect thesuction in the same way. It is another object of the invention toprovide a liquid pump that does not utilize suction and is independentof the vagaries of flow rate inherent in suction type pumping.

Further, in causing the liquid to flow, the suction must act against anyhydrostatic head that is effective. The liquid is commonly fed in avertical direction, usually upward but often downward. Any change in thehydrostatic head of the liquid sample will correspondingly change thenet or total eifective suction available for pumping the liquid. Suchchange occurs as the sample in a cup or in a funnel declines in level asit is consumed. This causes a gradual decline of the flow rate of theliquid. Another object is to provide a liquid pump in which the rate ofhow is independent of the quantity of liquid present.

nited States Patent illZQddZ Patented Dec. 3, 1963 "ice Further,uniformity of liquid flow rate depends upon constancy of the impedanceimposed upon the liquid by the capillary. This impedance depends uponthe dimensions of the capillary bore and upon the viscosity of theliquid. Anything that alters either of these will change the flow rate.Thus, particles caught in the narrow capillary will obstruct the flow,as will also a deposit gradually forming upon the inner walls of thecapillary. Blood plasma readily forms such a deposit. This difficultybecomes the greater, the smaller the capillary tube. Small tubes-i.e.,tubes of high impedance-are desirable in flame photometry because theypermit and require the high suotions generated by high gas pressures,which cause finer atomization and more efficient excitation in the flameand also suppress the effects of hydrostatic head, While keeping thesample flow down to the low rates necessary for optimal excitation ofthe elements in the sample. But realization of the best conditions inthese respect may require a capillary tube only -a few thousandths of aninch in diameter, which becomes clogged with extreme ease.

Capillary tubes also become clogged very easily by bubbles, whichrestrict the sample flow. These bubbles tend to deposit within thecapillary owing to the reduction of pressure experienced by the liquidas it enters. This phenomenon can be avoided by deaerating the sample orby adding wetting agents, but both expedients are inconvenient and canin fact be interdicted by the nature of the sample. Bubbles also formvery commonly by a hydrodynamic effect at the capillary inlet. If theinlet has sharp edges, the stream of liquid as it enters on firstapplication of the sample will, by virtue of its inertia, resist thesudden change of direction imposed by the geometry of the inlet, andtend to skip a small area on the inner wall of the capillary just abovethe inlet. An air bubble is thereby trapped. Deaeration will notalleviate this difliculty. In some types of atomizer the formation ofbubbles is one of the commonest sources of error. It is an object toprovide a pump in which the rate of flow is not a function of thedimensions of the capillary tubes, permitting the tubes to be selectedfor optimizing other 4 variables.

A pneumatic suction atomizer pumps liquid at a rate proportional to itsfluidity. Viscosity depends upon the nature of the liquid, theconcentration and nature of solutes dissolved in it, and thetemperature. Flame photometry is a relative or comparative method ofanalysis; the sample must always be compared with a standand solution.It is of prime importance that the sample and standard solutions flow atthe same rate. Since the sample is often of unknown composition, it maynot be convenient to prepare a standard having the same viscosity.Further, viscosity is a very sensitive function of temperature. Anyslight differences of temperature between liquids to be compared canlead to corresponding errors. Warming by the proximity of the flame orcooling by evaporation of a volatile solvent will introduce similarerrors. Another object is to provide a pump having a controllable flowrate that is substantially independent of the viscosity of the liquidbeing pumped.

Atomizers for commercial instruments should be as nearly alike in theirdimensions and characteristics as possible, to permit interchange andstandardization of analytical methods. The manufacture of atomizers having the desired close tolerances of performance is exceedinglydifficult, as the dimensions and smoothness of surfaces are verycritical. Although subjected to the most rigorous inspection, commercialatomizers are never truly interchangeable.

In the manufacture of atomizer-burners an eiiort is generally made toadjust the dimensions and prescribe the gas pressures in such a way asto assure that for most 9 analytical emissions the intensity will bemaximal with respect to sample flow rate. Unfortunately, differentspectral lines or hands or diiierent elements attain maximal intensityat different liow rates. Thus the prescribed pressures for a givenatomizer-burner are necessarily a compromise. A pneumatic suctionatomizer-burner does not permit simultaneous optimization with respectto all three variables: fuel flow, oxidant flow, and sample flow. Thisdifficulty is particularly marked with hot flames such as premixedoxyacetylene and most especially with oxygencyanogen, in which theslightest departure from optimal flow adjustment can very greatlydiminish the analytical sensitivity.

A pneumatic atomizer injecting sample directly into the base of a flame(an atomizer-burner) can operate only with flames of high burningvelocity or with pilot flames to maintain combustion, owing to thenecessary high speed of the emerging gas. In the case of oxyacetylene,which is particularly advantageous for flame photometry, it may bedesired to atomize the sample with premixed oxyacetylene. Owing todanger of detonation, such a mixture should not be compressed abovep.s.i.g. Since a mixing manifold must be interposed, there mustgenerally be a pressure drop between the pure acetylene and the mixture,wherefore the mixture itself is not readily utilized at pressures ashigh as 15 p.s.i.g. But suction and atomization become less efiicient atthe lower pressures. Further, if a pneumatic suction atomizer is to beused in a spray chamber with premixed oxyacetylene or oxyhydrogen, thehigh burning velocities of these mixtures entail an appreciable pressuredrop across the burner port. This pressure drop imposes a burden uponthe atomizer, acting like the hydrostatic head mentioned above.Accordingly, it is an object of the invention to provide a liquid pumpfor use with atomizer-burners in which the liquid flow rate is notdependent on burner geometry nor on fuel or oxidant flow rates.

The available amount of certain samples (e.g., blood from a smallmammal) may be so small as to be inadequate for flame-photometricanalysis with a given instrument. It is known that in an instrumentoptimized for emission intensity, reduction of sample flow rate does notentail a proportional loss of intensity. Indeed, a 10- fold reduction offlow may cause a loss of only 50% of the signal. The possibility ofadjusting the sample flow rate independently of the flame adjustmentwould therefore be valuable in conserving a scarce sample. But with theusual suction atomizers this is not practical.

In general, the invention contemplates pumping by means of a constantbut adjustable flow of gas provided by supplying gas under controlledpressure to a very fine leak. The gas emerging from the leak acts as apiston to force liquid from a closed cup through a small tube orcapillary to the atomizer. The cup containing the liquid sample may besealed by merely being presse against a soft gasket. The liquid thustouches no additional object except the atomizer to which very littleliquid adheres. In general, no rinsing is needed. By proper constructionof the cup holder and the mechanism for moving it, samples can bechanged in very rapid sequence.

It is an object of the invention to provide a pump for liquid includinga liquid container, 21 cover for sealing engagement with the container,an outlet capillary projecting into the container, an inlet capillaryprojecting into the container, and means for supplying gas at a constantrate of volume fiow through the inlet capillary for moving liquid out ofthe container through the outlet capillary. A further object is toprovide such a pump including a leak connected between a source of gasunder pressure and the inlet to the container with the leak having aflow impedance that is high relative to any impedance imposed upon thefiow of liquid, so that the gas functions as a piston displacing liquidfrom the container, with the gaseous piston being generated at aconstant rate. An-

other object is to provide a pump having continuously variable pumpingspeeds over a wide range of flow rates, with the flow rate beingsettable to any desired value within a range in a matter of seconds andwith different ranges being available by merely changing the leak in theinlet line.

it is an object of the invention to provide a pump which reduces thehazard of analyzing highly volatile and combustible material, such asgasoline, by flame photometry. A further object is to provide a pumpwherein the sample is fully enclosed and hermetically separated from thesurrounding air thereby prevent ng evaporation and change of temperatureand concentration.

it is an object of the invention to provide a pump suitable for use withatomizers and the like which eliminates the inconvenience of cleaning,washing, rinsing, or changing auxiliary equipment such as syringes,cylinders, or flexible tubing. Orny the sample cup, 21 simplecylindrical container of polyethylene or glass, need be rinsed betweenuses. Often a water repellent cup, such as one coated with a siliconewater repellent, can be simply shaken dry and requires no cleaning.Another object of the invention is to provide a pump for liquids that isinexpensive and requires no moving parts and one that can beincorporated into existing commercial flame photometers and otherinstruments with only minor modifications.

While the invention is described herein in conjunction with anatomizer-burner for a flame photometer, it is also applicable to otherfields such as chromatography, electrophoresis, and fermentation, whereaccurate control of liquid flow is needed, often at low rates. Theinvention is also useful as a means of supplying sample to otherspectrocltcmical emission sources such as the are and spark. The drawingmerely shows and the description merely describes a preferred embodimentwhich is given by way of illustration or example.

in the drawing:

FIG. 1 is an elevation view of the pump used in conjunction with anatomizer-burner; and

FIG. 2 is an enlarged sectional view of a portion of the apparatus ofFIG. 1.

An atomizer-burner it} is mounted on a bracket 11 by clips 12, with thebracket in turn mounted on a base 13. A tubular shield 14 with an accessport 15 may be mounted on the bracket 11 around the burner NE. Fuel,such as hydrogen or acetylene, is connected to the burner through a line16 and a combustion supporting and atomizing gas, such as oxygen, isconnected to the burner through a line 17. Suitable pressure regulatorsand rate of flow control valves may be positioned in each of the linesfor individually controlling the fuel and atomizer gas flow rates. Asmall diameter tubing or capillary 13 is fixed within the burner andprojects downward through the bracket 11 and a gasket 1% fixed to theunder side of the bracket. Typically, the tubing 18 will be a shortlength of stainless steel hypodermic tubing.

The internal arrangement of the atomizer burner 10 is shown in detail inFIG. 2 and may be identical to that shown in my previously mentionedpatent, No. 2,714,833. The upper end of the tubing 18 terminates at thedischarge nozzle 2b. The line 17 for the atomizer gas communicates withan internal chamber 21 which terminates in an annular opening about thetubing 13. The line 16 for the fuel communicates with another internalchamber 22 which terminates in an annular opening disposed about theatomizer discharge nozzle 2'3.

Another tubing or capillary 25 is fixed to the under side of the bracket11 and projects downward through the gasket 19. Typically, this tubingis also a length of stainless steel hypodermic tubing. Means areprovided for supplying a gas at a constant rate to the tubing 25.Ordinarily, this gas will be the same as that used for the atomizer andoxidant gas and, hence, usually will be oxygen. In the embodiment ofFIG. 1, a source of oxygen under pressure is connected to a line 25having a pres- 5 sure regulator 27 therein. The output from theregulator is directed through a bypass valve 2 3 to the atmosphere andthrough a shut-off valve 29 to a leak 3d. The leak is connected in turnto the capillary 25. A pressure gauge 31 provides an indication of thepressure at the output of the regulator 27.

A container 34 is removably mounted on a platform 35 for movement upwardinto engagement with the gasket 19. One preferred apparatus for rapidlyraising and lowering and changing the container is shown in FIG. 1. Thecontainer is held onto the platform by spring clips 36. The platformmoves up and down along four guides 37 which, in turn, are supportedon aplate 38. A lever 39 is pivotal'ly mounted at one end to the platform35. Another lever 40 is pivctal ly mounted between the plate 38 and acentral point of the lever 39. The two levers are dirnensioned to coactas a toggle for locking the container in the upper position, as shown insolid lines in FIG. 1. The lever 39 may be manually rotated to theposition shown in phantom lines in FIG. 1 to lower the container. Whenthe container is lowered, the plate 38 may be rotated about the post 4 1for removal and reinsertion of suitable containers.

The leak 39 has a very high flow impedance in comparison to the tubings25 and 1-8 so that the leak substantially controls the rate of how gasinto the container 34. Typically, a leak consists of a length of a noblemetal wire 44, such as palladium, sealed into a hard glass capillarytube 45. The leak will be a few centimeters in length. The capacity orflow rate of the leak is a function of the diameter and length of thewire and the area of actual contact between the metal and glass. Typicalleak rates for use with an atomizerburner range from 0.03 to 0.2ml./rnin, per 1 psi. pressure drop across the leak. The rate for aparticular leak can be varied by varying the setting of the valve in theassociated pressure source. Diiierent ranges may be obtained bysubstituting leaks of different lengths or difierent wire diameters.

Other examples of suitable leaks include a pinched metal tube, a veryfine glass capillary, and a narrow tube packed with fine powder.

Typically, the pressure regulator 27 will be set to provide an outletpressure in the range of to 3G p.s.i. As the gas flow rate through theleak into the container is extremely small, it is preferred to operatethe system with the bypass valve 28 partially open to provide a higherflow rate through the regulator so as to improve the regulatoroperation. The bypass valve 28 also permits rapid bleeding of the systemon reduction of pressure to diminish the pumping rate without waitingfor the gas to escape through the leak 30.

in operating the apparatus, the fuel gas and atomizer gas flow rates areadiusted to the desired values. A container with a standard liquid israised into engagement with the gasket 19 and the rate of flow of liquidup the tubing 1-8 is adjusted to the desired value by choosing anappropriate leak and suitably setting the regulator 27. Then thecontainer is lowered and a container with a sample liquid is placed onthe platform and raised into the operating position. The flow of gas tothe fuel line, the oxidant line and the pumping line is not interruptedas one liquid is substituted for another. After the appropriatemeasurements are made, additional sample and/ or standard liquids areplaced in containers on the platform and raised to the operatingposition. The apparatus may be operated with various quantities ofliquid in the container and containers of varying capacities may beutilized. Of course, all the containers must have approximately the sameexternal dimensions so as to fit onto the platform and engage thegasket.

When a container of liquid is raised to the operating position of FIG.1, the incoming gas from the capillary functions in the nature of an airpiston forcing the liquid down in the container and up through theoutlet capillary 18. The contact pressure between the container and thegasket must be sufiicient to provide a hermetic seal adequate to retainthe pumping gas. In this apparatus, the rate of flow of liquid up thecapillary 13 is independent of the rate of flow of gas in the fuel line16 and in the oxidant line 17. As the liquid is forced through theoutlet capillary, any tendencies for this line to clog, as referred topreviously, are substantially Without eiiect. Also, since the rate offlow of liquid is not a function of the size of the outlet capillary, arelatively large diameter tubing can be utilized.

It should be noted that in operating the apparatus, a transientcondition in the rate of flow of liquid up the outlet capillary occurswhen the container is first raised into position. In a practicalembodiment, the time constant of initial equilibration can be kept toabout one second, which is equal to that often incorporated in themeasuring system of a flame photometer to damp fluctuations of theflame. Apparatus constructed according to the embodiment of FIG. 1 ispresently in use to provide liquid flow rates in the range of 0.01mL/min. to 3 ml./min. and the apparatus of the invention may beconstructed to provide flow rates which exceed this range in bothdirections.

Although an exemplary embodiment of the invention has been disclosed anddiscussed, it will be understood that other applications of theinvention are possible and that the embodiment disclosed may besubjected to various changes, modifications and substitutions withoutnecessarily departing from the spirit of the invention.

I claim as my invention:

1. in a pump for liquid for an atomizer or the like, the combination of:a liquid container; a cover for sealing engagement with said container;an outlet capillary projecting into said container; an inlet capillaryprojecting into said container; means for supplying a gas at a constantrate of volume flow to said inlet capillary for moving liquid out ofsaid container through said outlet capillary, said means comprising agas leak connected to said inlet capillary with said leak having a flowimpedance that is high relative to the fiow impedance of said outletcapillary; and a shutoff valve only upstream of said leak forcontrolling the pumping of liquid by said pump.

2. In a pump for liquid for an atomizer or the like, the combination of:a frame; a liquid container; a cover mounted on said frame; containersupport means carried on said frame for lifting said container intosealing engagement with said cover; an outlet capillary carried by saidframe for projecting through said cover into said container andterminating adjacent the bottom thereof; an inlet capillary carried bysaid frame for projecting through said cover into said container andterminating adjacent the upper edge thereof; a source of gas underpressure; and a gas leak connected between said source and said inletcapillary for supplying gas at a constant rate of volume flow thereto,with said leak having a flow impedance that is high relative to the flowimpedance of said outlet capillary.

3. In a pump for liquids, the combination of: a sealed container for theliquid to be pumped; an outlet capillary projecting into said container;an inlet capillary projecting into said container; and means forsupplying gas to said inlet capillary at a constant rate of volume flowfor moving liquid out of said container through said outlet capillary,said means comprising a gas leak having a fluid flow impedance that ishigh relative to the iiuid flow impedance of said outlet capillary.

4. in a pump for liquids, the combination of: a sealed container for theliquid to be pumped; a liquid outlet line communicating with saidcontainer; at gas inlet line communicating with said container; and asource of gas under pressure connected to said inlet line, said inletline including a gas leak connected between said source and saidcontainer for supplying gas at a constant rate of volume fiow thereto,with said leak having a flow impedance that is high relative to the flowimpedance of said outlet line.

5. A method of pumping of liquids in a continuous and uniform stream forfeeding to an output device such as an atomizer-burner or the like,including the steps of:

maintaining the liquid to be pumped in a closed volume with an outletopening;

introducing a gas into the closed volume at a constant rate of volumefiow to eject liquid from the volume through the outlet opening; and

directing the ejected liquid directly to the output device.

6. A method of pumping liquid in a continuous and uniform stream forfeeding to an atomizer-burner with the rate of flow of liquidindependent of changes in how impedance of the atomizer-burner andindependent of the rate of flow of fuel, including the steps of:

maintaining the liquid to be pumped in a closed volume with an outletopening;

introducing a gas into the closed volume at a constant rate of volumeflow to eject liquid from the volume to the outlet opening; and mixingthe ejected liquid with the fuel at the nozzle of the atomizer-burner.

References Cited in the file of this patent UNITED STATES PATENTSSchlauch Sept. 2, Savage Feb. 18, Conklin Oct. 18, Shields Nov. 20,Hawley Sept. 28, Knapp May 13, Swartfiguer July 13, Gilbert Aug. 9,Gauthier et a1 Feb. 5, Marantz Nov. 19, Jones Mar. 22,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa tent N0. 3 112882 December 3 1963 Paul Thomas Gilbert Jr.

or appears in the above numbered pat- It is hereby certified that err esaid Letters Patent should read as ent requiring correction and that thcorrected below.

line 18 for "respect" read respects second occurrence read of readp.s.i.g second occurrence.

Column 2 column 3 line 3 for "or", column 5 line 44, for "pQs.i" column7 line 3 strike out "of",

Signed and sealed this 5th day of May 1964.

(SEAL) Attest:

ERNEST Wo SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

3. IN A PUMP FOR LIQUIDS, THE COMBINATION OF: A SEALED CONTAINER FOR THELIQUID TO BE PUMPED; AN OUTLET CAPILLARY PROJECTING INTO SAID CONTAINER;AN INLET CAPILLARY PROJECTING INTO SAID CONTAINER; AND MEANS FORSUPPLYING GAS TO SAID INLET CAPILLARY AT A CONSTANT RATE OF VOLUME FLOWFOR MOVING LIQUID OUT OF SAID CONTAINER THROUGH SAID OUTLET CAPILLARY,SAID MEANS COMPRISING A GAS LEAK HAVING A